There's certainly a difference. In the first sentence, you are asking her to get herself ready. It could be you're taking her on a long trip and you want her to get her belongings all packed and ready, by Friday.
In the second sentence, you are asking someone (a third party) to get her readied. It could be you are taking her on a long trip again but this time, you want someone, maybe her mother, to pack her belongings and get her ready for you, by Friday.
The meaning timebomb sees in #2 is definitely there. They can mean the same thing, but the second construction omits any mention of agency, and it's not clear who you expect to do the job of getting her ready.
The connecting-verb-adjective form "to be ready" has some disadvantages of the passive-voice construction it resembles. So the question of someone else "readying" her is raised. Yes, you can argue, there's no indirect-object "someone" indicated by "for," it's clearly the participial half of a verbal phrase, "to ask for." The problem is clarity, and in a clear statement the grammatical correctness of some part of it shouldn't have to be argued.
Try an active-voice example and see the difference:
"I'm asking her to reconsider."
"I'm asking for her to reconsider."
There the meanings are almost identical, and this points to the other thing in your sentence that is indecisive, and allows variant meanings to be inferred-- the choice of "ask for" over the blunt "ask." It's politer, not so much a "direct order" than a "do it for me" message.
I get the impression you're saying "I asked her to be ready," and I agree with timebomb that that's the best way to say it.