This.
The £90 could be her direct debit amount, set to start paying for her winter heating. It could be right or it could equally be too low or too high, it's impossible to say without information about the size, type of insulation, type of heating, how much she uses it and likewise for things like cooking, laundry and showering.
But unless she is quite frugal with all these things, it's unlikely to be significantly less than £90 and could be far more when averaged over the year.
Last Christmas a relative, who lives in a very small purpose built 2 bed flat mentioned that their electricity bill for the cold December had been nearly £800. That's 9 months worth of DD payments gone, right there, with another 11 months of usage to pay for.
But it's still a red herring and not the issue you should focus on. If she is struggling due to her income not meeting her basic expenses, you filling the gap for her is not the answer unless you can afford to and want to.
What happens when she is short next month, and the one after that? She needs to review her budget and try and make it work, seeking advice about checking for benefits, working more if she can and reducing her costs so her money goes further.
Or she could be a cheeky fucker who's spent all her money and now wants to spend yours too. It's always the electricity, or food they can't pay, they don't talk about how they spent the electricity or food money on non essentials.