Hi A.!
Potty training is somewhat of potty leading for me, you have to, in a way, follow your daughter's cues, you will know when she is ready, if she is comunicating she is unconfortable with a dirty diaper etc, if she is able to pull her pants or undies up and down by herself, etc and I think mentally ready for the change. Girls are faster than boys, I know that, my sons have been potty trained by 3 years old ( your MIL would flip!), but you know what one thing is certaint, if you push it she will have an adverse reaction,(you said she is ALREADY scared of it) and guess what, it WILL take longer and you will have to clean a lot more messes. Your MIL needs to respect your wishes on the subject. If you are not reinforcing potty trainig yet and she is, your daughter will only be confused and again, it will take longer. When she is ready, beleive me , she will be trained in less than a week, if you start too early may take you months. Talk to grandma, and stand firm on your graunds. Another suggestion, I never used the potty, I used a ring to put in the toilet and a stool, that way my kids knew where to go from the begining and it was a lot less messes to clean for me!! Make it fun when she is ready, buy a book, put a sign in the bathroom with her name on it, make a big fuss the first time she goes ( I baked a cake for my first son's first time...I little too much I know! haha) I mean, praise her and show her how praud you are, and if gramdma wants to help, she HAS to go along with your program.
Good luck with everything and I pray that your husband is kept safe in Iraq and he comes back soon
A..