Sorry; usually not liking to be handled is a problem for new piggies - you didn't mention for how long you have had her.
You would have probably have noticed little balls forming in her belly if she was pregnant considering you are handling her regularly. She would be near giving birth considering the length of time you have had her and would look most likely somewhat pear shaped now. Only rarely does a sow not show when she only has one baby. I have handled sows on the day before they gave birth and there was no difference in behaviour.
It can be just a one off; otherwise, I would look for something like mites (many piggies don't like being touched then as the skin is very painful).
Weekly weighing is a very good way of keeping an eye on your girl's health as you can spot problems early on when they are much more easier to treat.
This is a good link to what kind of weight loss needs what kind of attention:
http://www.guinealynx.info/weigh.html
It would be great if you considered a friend for your girl, even better if you'd think about finding a rescue that allows you to bring your girl to choose her own new friend herself so you can be sure that they will be best of friends! Both sows or neutered boars are an option. You will love the lively, vocal interaction and the group popcorns when they egg each other on!
Here is a map of recommended good standard and practice rescues. All piggies from any of these rescues will be health checked, properly sexed, guaranteed not pregnant (they go through a 10 week pregnancy watch if they are not born at the rescue) and virtually all rescues offer piggy dating. A good rescue will also give you support during the settling in period and throughout the life of their piggies. That is a LOT more than you get in a pet shop and is worth a bit of travel!
https://maps.google.co.uk/maps/ms?msid=209994852075231951564.0004b8fd9391b4257d8eb&msa=0