I have to disagree, i've been breeding guppys for years and even in the most pregnant of guppys i have had, none has ever shown a spine like that and turned out to be healthy- she doesn't look like she has a massive amount of fry in her. The spine clearly looks distorted to me, it really isn't natural or healthy to be like that.
If it makes you feel better, you can keep her alive, but the longer you keep her, the more distorted the spine will become. It you choose to keep her, i would strongly advise isolating her in a different tank away from the other fish to help prevent her passing on anything towards them.
I will try and get you a pic of one of my mature female guppys who is hevaily pregnant as you will then see that your guppys bent spine is not a result of pregnancy or old age.