At 3.5 I would go for the surgery as long as she is still active and otherwise healthy. Prolonging the surgery only allows the tumour to continue growing.
Surgery is always a risk, but I don't consider 3.5 to be too old or the risks to be too high. If she was a year or more older then I'd be more hesitant.
Basically it's you have two options. Do the surgery which carries a small risk, but could cure her, or leave the tumour and her death is certain and possibly not that far away depending on how the tumour grows.
* * * Nancy * * *
Retired from breeding
Rescue contact for both the Hedgehog Welfare Society and the IHA
Rescued over 70 (and counting) hedgehogs needing a new home