The OPK's will only tell her if she'd having the luteinising hormone surge that immediately precedes/causes ovulation. If the test is -ve she won't know if she did or not, and if she keeps using them to see if she is, and she doesn't, the pregnancy could be well established and it'll be too late to have emergency contraception.

Some antidepressants and anxiety drugs can affect embryos, only her doctor will be able to tell her if hers can. The damage is more likely at this early stage though, when bubs basic structures are forming.

HTH