The Royal College of Speech and language website (rcslt.org) will have a list of all the universities offering accredited courses and apprenticeships. Undergrad courses will be 3 or 4 years. Acredited courses can still have a slightly different focus - some are more linguisticsy or social sciency and some more medical sciencey, so she should look at what she likes best - some courses will be in uni department of social science, others in healthcare science, or even medicine - I think Newcastle it is part of the medical school.
She is likely to also need either some experience of shadowing an SLT so she understands the role, or some work/ volunteering experience, eg with young children or in a care home etc.
Universities are likely to interview candidates, so she should be prepared for that.
Good A levels could be English language, psychology, sociology, MFL, sciences, maybe drama.
Like other allied health courses, she will be on placement over a wide geographic area, so learning to drive might be helpful.
The NHS offers a learning support fund to help with some costs, such as placement travel expenses, as long as you are UK student and have applied for student loan.