We've talked about this before and opinions vary, it depends on a number of things.
I sold my mother's house when she came to live with us as the costs of making it rentable were just too much, it was (a bit) run down. It needed about £6,000 spending to bring it up to scratch, get the gas and electricity checks done and insure and using an agent would have netted about £600 a month so the first year would have been pretty much break even. The income from the rent would reduce any means tested benefits and is liable to income tax so combined with her pension it would put her over the threshold for income tax so probably 20% of the income would go in tax and guess who would have to do all the self assessment forms.
I decided it wasn't worth the grief but I know many on here do it quite successfully, get a good tenant and it's OK get a bad one and next time you visit the house will be after you've sent the bailiffs in to see how much the place has been trashed.
There could be CGT implication but you have an allowance of about £11k a year and you can roll years over to the next year so unless it's some flash gaff in central London doubling in value every year CGT isn't likely to be an issue, you'd have to get the house valued before you rent it then any increase in value would be from that time to when it actually gets sold would be liable to CGT less her allowance.
All the costs of running the house; insurance, repairs, agents fees, improvements can be deducted from the income before tax is calculated but it does mean the dreaded self assessment procedure.
I just decided it was easier to get the money in the bank, but as I say other do it and make it work, I think it matters where you are and how much rent you will generate.