Horses can only train 5 times a week, so maybe you trained her 5 times instead of 2 or 3? Click on the little dumbbell on the horses page and it will tell you how many times shes been trained this week 

Good morning,

Thank you for your reply! I just discovered that on the WIKI, which in my opinion is a TOTAL nonesense.

Why on earth would training be limited to 5 times a week and can be performed by 5 clicks in one training session? And then what? What are we supposed to do the rest of the days? Just feed and water the horse, that's it? If so, too bad then, for I can't see myself coming back and forth to just care for the horses without any improvement!

You can show horses too, and breed them. Sell them, auction them.

Your supposed to rest the horse on the two off days.

One click is one training session, not five clicks.

Your supposed to train a horse once a day.

*sigh* ....for now i'll assume that you're not trying to ragebait us on purpose:

as KayTea said above, there are definitely other things you can do with horses. halter shows are great for horses with good Breed Standard stats (3 stars or higher are often best for halters, but you can also halter 1 star and 2 star horses if you wish). halter shows take up 20% energy each.
otherwise you can discipline show which is dependent on your horse's stats. each disc show will cost 10% energy.
additionally there are careers, all accounts have the model horse career unlocked by default so you don't have to buy it. you can send horses for a career every half hour and it costs 20% energy each. careers are considered best for starting players because unlike the previous two you can't lose money from careers. the tradeoff is that it doesn't give as much money.
lastly, you can use your horse in explore, there isn't a wiki page on the hoofbeat plains yet but it's pretty simple. you just select a horse and move around the map to find items, quests, or wild horses. one step from your horse takes 2% of their energy, while one action you take (pick up item, attempt wild horse capture, etc) will take up 5% of your player energy.
breeding also takes up energy, 20% per attempt at breeding. your horse being bred by another player doesn't take away that horse's energy, so you're free to list your horses up for stud without worrying about their energy being taken up.

if you're not able to do any of these, common reasons are:
can't halter: you need to register your horse in a Breed Registry (for purebreds) or a game owned club (for recognized crossbreeds, generic "unnamed" crosses cannot be registered to these)
can't discipline: disc shows run at 1am/7am/1pm/7pm every day and sometimes take about half an hour to refresh, if you come back later you should be able to enter.
can't career: your horse needs to have their personality tested at the vet before they can career.
can't explore: go to your horse's page and click the pencil icon on the top right to edit your horse's info. then scroll down to Working Paths and make sure "Explore" is checked. this can also be why you're not able to do any of the above, make sure any other paths you want to use your horse for are checked.
can't breed: mares have a 7 day cooldown before they can breed again while stallions have a 2 day cooldown. you can check your horse's cooldown by going to their page and scrolling down to see the "Times" section in the bottom right corner.

it's best to train all five times in one day, because the 5th training session will activate a 7 day countdown that after finishing will allow you to train again in a week. so for example, if you trained all 5 times on a Monday, the next Monday you would be able to train again. however if you trained once on Monday and then once every day after that, your final training session would be on Friday. you would not be able to train your horse again until the next Friday, meaning your horse could have been trained much earlier.

the gameplay loop of HoFa is basically to train 5 times a week and then make the best use of your horse's energy throughout the rest of the week. what you do with that energy is up to you, it really depends on what you're trying to use the horse for. if you plan to breed the horse it's probably better to show them as much as possible and breed them later in life so you can have foals with good Training Boosts and stats. a high TB will mean more stats earned for each training session. you can also just career horses to gain their levels though it can be a bit slow depending on the horse. if you want to collect items and wild horses then exploring hoofbeat plains is best, you don't really have to worry about training as much if you just explore.

the help page is currently broken for some people but if you have any questions there are quite a few people happy to assist you if you ask kindly. you may not get an answer right away as people have their own lives and jobs to worry about and there's different timezones, but some people like me are online at least once every day and can help out.

@Dave24, bro? There's literally tons of other things to do with your horse. You can breed it, show it, auction it, etc (just like @KayTea said). You obviously either skimmed or disregarded the wiki as you have no clue how this game works or what to do (anybody who went through the wiki would know how to play & what to do). Please don't ragebait us! We will not give you a warm welcome that way!