Need advice on mammary tumour 8y/o female shihtzu

[Lapli41]

Hey guys, looking for some advice..several wks ago my boyfriend found a small, airsoft BB sized lump on our shihtzu, under one of her nipples. She's 8-9yrs old, never been spayed (im a big spay/neuter advocate but he had her for about 3 yrs before we even got together,and i never managed to twist his arm into letting me get it done) i had other sick dogs so it was another week or two before i got her to the vet & it had grown to be pea-sized. All he really did was feel the lump, and present me with two options - leave it alone, or do a very quick surgery and remove it, hope no more show up. Again, she's almost 10 and has never had surgery before - what would you do if it were you? My worst nigtmare is that after consenting to do the surgery, what if she reacts badly to the drugs and dies on the table, alone, over a surgery she didn't REALLY need? My other worst nightmare is doing nothing and then finding out further down the road that she has cancer that the surgery could've prevented/slowed. Please please, help me!