Can my daughter still be eligible in F2A visa, which is available right now?

Once her petition was filed before she turned 21 years old and she is unmarried, her 21 years will not affect her eligibility for a visa in the F2A category. Under the Child Status Protection Act CSPA, her age will be frozen to the date her I-130 was filed notwithstanding that she has or will turn 21 years before her case is adjudicated

If you are a permanent resident wh has filed for your daughter, then, yes, your daughter is eligible for a visa ion the F2A category. However, her petition has to be approved first. It is unlikely that the F2A category will stay current long enough for your daughter. It would take a detailed analysis of all the facts to determine whether your daughter would be eligible under the Child Status Protection Act for a visa in the F2A category later when she is 21 or older.