What type of lawyer does she need?
She needs a litigation lawyer. This is a civil matter, not a criminal one (though there may be underlying criminality).
EDIT: she needs a solicitor*.
It sounds like the claim lies in contract law – both as to how and with whom the contract was made, and what factors induced your colleague into parting with the money.
It falls into the small claims court, which means that each side has to bear their own costs (unless the court finds in her favour – she needs legal advice on how to make that happen if nothing else).
How do you set about finding one?
Ask Citizens Advice if they have any contacts at local legal firms. TBH, you need someone who has experience doing civil litigation, but who is cheap enough to justify it (at £3.5k, it’d be easy enough to rack up more in costs).
She does need legal advice. It’s worth paying for. And she might be able to find someone to do it on a contingent fee (no win, no fee) basis.
*There are three types of lawyer in England and Wales (not sure about Scotland): solicitor, barrister, notary. Roughly speaking, if you need legal advice, you go to a solicitor. If you’re in litigation (civil or criminal), your solicitor may need to instruct a barrister. Notaries are usually used these days for making documents enforceable in other jurisdictions.