Personally, I don't think a tour is necessary.
We liked China so much we're heading back there next August.
Admittedly, we are not both female - but being over six foot and with long blonde hair the Chinese take a special interest in me (expect a lot of impromptu photo calls). We met a lot of lone female travellers in China and none reported any problems. If you do get stuck there are usually always a few foreigners about who you can tag along with. The travelling community we met in China was really supportive - its also a very easy place to meet people because of this.
We found that China was actually very easy to travel round by train. Pretty cheap too. While they don't always arrive when you might expect them too, we never encountered any trains that departed late. Just don't set deadlines for when you need to arrive and you'll be fine.
We always opted for soft-sleeper class when it was available. To be honest, the only difference between soft-sleeper and hard sleeper is that in hard sleeper you are in a compartment with 6 beds rather than 4 and there's not always a door on the compartment. This means that in hard sleeper the sound - and much worse - the smoke, drifts in from outside.
The worst bit about travelling by train is buying the tickets. The stations can be huge, crowded and confusing -but if you can just stay relaxed and accept the fact that you are going to be stared at by hunderds of people then you'll be fine. The Chinese people we encountered were very friendly when approached and went out of their way to help. I found that if I drew some pictures describing what tickets I wanted it not only got a giggle from the station staff but people crowded round to see what the giant blonde foreigner was up too and how they could help. I also had some words of Mandarin - like "softsleeper" printed out from a website to make life easier.
The important thing is to be clear about what you want and ask for it with a smile - no matter how grumpy the counter staff look. Internet cafes are everywhere and you can use websites such as Seat 61 (http://www.seat61.com/China.htm) to plan what train number you need to get - or simply ask the receptionists at your hostel or a hotel to give you a hand.
Obviously that is based on our limited experience and the usual caveats apply (don't trust everyone, stay with the crowds, keep your valuables well concealed, etc, etc) and I'm sure there will be plenty of people who can tell you about bad experiences they had in China - but isn't that true of travel in any country? Ultimately, its up to you to go there and decide for yourself.
I hate to end on a quote, it's insanely cheesy, but what the hell:
"Don't be afraid to go out on a limb: that's where the fruit is".