Your wife cannot collect on your record until you reach an age which you can collect SS (age 62). I actually believe you have to file for SS and then suspend benefits when you reach 62.
If your DW decides to collect on your record (by waiting until you reach 62), everything is based on your PIA. So, if she is FRA, she gets your FRA benefit @ 50%, as long as you are eligible to receive benefits. See section 724.1 (d)
I don't believe they would allow your wife to refile to collect on your record once she has elected to collect on her's. I could be wrong (and I hope so since my DW is 5 yrs older than me).