To add a few more thoughts to those of others. I am a city lawyer, (solicitor).
I would personally advise against aiming for the bar if it is criminal or the likes. Usually slightly less competitive, but awfully paid unless hugely successful. I suppose if you are superbly intelligent and can get a double first etc, then the doors of chambers practicing Chancery and Commercial will be open. Chancery or commercial are probably the only only areas worth all the slog for, as they pay very very well.
On average, I'd say to get into these fields you need to be much more well qualified than the average trainee in the city.
If you are bright enough to gain pupillage as a criminal barrister in London, then you are likely suitably qualified to gain a training contract, and make much more money.
Of course, this is considering a career choice purely from a financial reenumeration perspective. If one is willing to have a lower salary but the work is more satisfying to them, then go for it!
As to answer the OP, I would advise that she decides if she has a passion for advocacy, if she does not, and does not realistically look like a starred undergraduate, then a solicitors firm is probably better, and safer option.