Diet questions

I have a sow that may be possibly pregnant. I adopted her from someone on new years eve. I emailed her on the 6th because Marmalade was gaining weight and i thought maybe i was feeding too much. She told me that there is a possibility that she may be pregnant because she had her with a male before christmas. The lady found out just after christmas that she was pregnant with twins and decided to re-home some of her piggies.

My question is, I am not totally sure she is pregnant. Can i, to be safe, feed her alfaalfa pellets for 2 months to make sure any possible babies are nutrient rich and if by the middle of february she isn't showing signs then switch her back to timothy pellets?

Question 2: how long after the babies are born should she be on alfa alfa pellets?