You know much better about Bitcoin than your neighbor so I think, it's pretty good if you give her advice.
All I can say on this whole story is, "
Invest of what you can afford", because investment in crypto or in Bitcoin need to be patient and it could be take in a long-run process of holding.
Could this be a brilliant decision or did she act without caution?
If she can survive financially in a long run, that could be. Bitcoin investment might give a better profit but there's no time frame when it will happen.
Is it really wise to trade her funds in this direction?
Not so, if the amount that she willing to invest in the amount that I have mentioned above.
If she was to split the funds in purchasing other coins it would have been appreciated as well but all she wants to buy is bitcoin.
The safest investment, in the long run, is Bitcoin, IMO, there's no need for other coins. Just focus on Bitcoin.
If she doesn't have another source of income aside from that taxi driving, it's better to secure first his daily financial needs with a stable source of income than gamble it is investing into crypto.