Leaving a female cat unneutered is far far more dangerous than the risks of anaesthetic and spaying. Cat's are induced ovulaters and as such don't have periods, this means the uterus doesn't clear itself out and each time a cat comes into season the risk of infection, called pyometra, increases. Pyometra is potentially fatal.
On top of this an unspayed female is at increased risk of developing female cancers.
Female cats as well as males can spray urine to scent mark, if she's spayed she has no reason to do this as she's no longer trying to atttact a male by making your house stink. A cat in season is also a good escape artist. You may think she's safe indoors but it takes one split second mistake and she escapes and then you risk her catching feline leukaemia, feline version of HIV and of course pregnancy.
Finally it's just plain cruel to leave her unspayed, can you hear how desperate she sounds in that deep crying sound she is making? That's because her instincts are telling her she absolutely NEEDS to mate, a cat in season usually won't eat, play, sleep well etc. as all they want is to call the male. Not because they enjoy mating or pregnancy, it's actually dangerous and painful for female cats but because they cannot ovulate without mating. She will come into season quicker and quicker if this doesn't happen and can end up where she is basically never out of season and will lose weight and condition rapidly.
Honestly she needs to be spayed, the benefits far far far outweigh the risks!