"Ella sólo había tomado vino."
Translation:She had only drunk wine.
If "she alone" (only her, out of the group) had taken wine, we use the adverb "sólo", which doesn't react to gender, and thus does not change its form. The same adverb is used for "only wine".
If she had "taken wine alone", then we use the adjective "sola" (and solo for a male), as adjectives must agree in gender and number with the noun they modify.
Ella sólo habían tomado vino.
- She had only taken wine.
- (tomado: taken/drunk; bebido: drunk)
Sólo ella habían tomado vino
- Only she (she alone) had taken wine.
Ella habían tomado vino sola.
- She had taken/drunk wine alone.
Él habían bebido vino solo.
- He had drunk wine alone.
To be fair, I completely agree with that sentiment, but that is because we are educated on the subject, not because it is wrong. Descriptivism allows for mass changes in language like that; it will probably eventually be viewed as correct and people like us will have to learn to deal with it.
Native speaker Mabry says above that "solamente" is "weird." I.e. not commonly used.
Colton, hola. I don't know who down-voted your comment, but it could be to remind you to turn off your "Caps-lock" key (because that is considered shouting), or to read comments already posted in the forum before you add your "voice." Many times your question has been asked and answered by a lot of people who have taken their time to explain, but do not want to have to explain to more and more people over months or years later.