There's no specific period but if you obtain credit when you are planning to declare BR in the near future this could result in a BRU.
If you're situation changes then there is not a lot you can do i.e. you have a loan in Feb 09 but in Apr 09 you lose your job then it shouldn't be a problem. But if you get a loan in Feb 09, spend all of the money on holiday's, etc. and then declare BR in Apr 09 this would definitely be frowned upon.
She should be fine but you should advise her to contact the CAB, CCCS or National Debtline as they will be able to discuss her situation and solutions.