Please step in with offering additional syringe feed (pellets soaked in a little water will do) to get her over the turn of the year.
Try to ease the syringe in from the unaffected side in order to minimise the discomfort.
All About Syringe Feeding and Medicating Guinea Pigs with Videos and Pictures (you can find practical tips in chapter 3)
Consultation fees will be lower during regular opening times, which will bring down the cost quite a bit .
You can also ask to take her home with you afterwards in order to cut cost further and bury her in a flower bed or in a planter underneath a little shrub or hardy perennial if you have a balcony, a backyard or a private entrance.
Make sure that you dip her feet in safe ink and take her foot prints on a pieve of paper or get some kids plastocene instead. Cut a lock of her hair if you want to opt for a tangible reminder.
I hope that helps you of make the best of the time left to help you for the time after. 6 years is an excellent age and a testament to your good care.
HUGS