A bike fitting is never a bad idea and usually results in far greater comfort on the bike, which in turn leads to, more bike love and more riding.
Without knowing the specifics of your choices, it's really hard to give you any feedback on that. A lot of women here have used Specialized's BG or Tru Fit services and had positive experiences, myself included. (you don't need a Specialized bike to use this service). You may also want to do a search on this forum because bike fitting has been discussed a lot.
Happy riding and welcome to TE!
2001 Trek 7500 FX, converted to a hauler - Serfas
200? Marin hybrid - Selle San Marco
2004 Trek 5200 - Avatar
2011 Trek 6.2 Madone - Ruby