One of the problems with tax and NI if you are self-employed is keeping up to date with the annual (and other) changes to rates, allowances and other things, which is where an accountant will be bang up to date, as well as with allowances for expenses and the purchase of "capital" items, plus allowances for use of car, office at home etc. It may cost a little (but at the lower end of accounting charges unless the trade is unusual) but should be well worth it. Keeping good records will reduce the Accountant's time (and fees) considerably.
If her profits are below the £6,725 level, self-employed NI contributions are not payable at all - and hence do not secure entitlement to the state pension. The alternative is to pay voluntary contributions currently costing £17.45 per week (as opposed to the self-employed rate of zero for profits between £6,725 and £12,570). If profits are above the latter figure there is also Class 4 NI to pay of 6% of profits. Despite being called "National Insurance Contributions" Class 4 NI does not qualify you for ANYTHING AT ALL - it is effectively an additional tax on the self-employed.
Another problem with not having an Accountant is knowing what expenses are claimable against your profits and whether the purchase of capital items can or cannot be claimed.
Most towns of any size will have a firm of accountants who will not charge the earth. Often retired accountants (like me) will do the job cheaply in order to keep their skills honed - we have to do that to keep our qualification current. I even do the accounts for some clients free of charge (but don't tell the others!).
As she is already doing some self-employed work she should already be registered as such with HMRC - that is a priority.
Good luck to her.
In fact, one of my "free" clients is a lady with RA. For a lot of her life she was too ill to commit to an outside/regular job but managed to make a decent living for herself. She is a singer - you might have heard her singing some of the commercials on the telly! And no, they don't pay much! I could mention another well-known situation that many of you might have heard her voice but I won't!