Personally, I would not want another snake in with an incubating female. Regardless of what your local expert may have told you, ball pythons are not social animals. Had she been able to lay her eggs in a secluded spot, away from the other one, she would have done so.
CAN you house two BPs together? Of course....but people will recommend against it, and for a number of good reasons. Can you keep all 5 babies in one tank? Same answer, with largely the same reasons...except you are more likely to experience issues with the babies.
Candling the eggs (shining a light into them, to check for veins) was mentioned earlier - I will recommend against, until you are committed (and ready) to put the eggs in an incubator. The more times you disturb Mom or the eggs, the greater the likelihood that she will abandon them. That isn't an issue when you're transferring them into a ready incubator; but it is when you don't even have an incubator. (Some are better mothers than others, and will keep returning to their eggs; others will bail the first time they are lifted off them).
Reptibator - I had forgotten about this one. I have no experience with it; but will say that it looks to be somewhat better than other entry level options. Typically, with incubators of that type, fairly consistent room temperatures are required...I would expect that with the upgraded thermostat, this will be more tolerant of daily temperature variation; but the company's own recommendation is that it be placed in a cooler room with consistent temperatures - which can be difficult for many to achieve in mid summer. If the eggs are adhered in a pile, you may find that the top eggs are closer to the heating element than you want. I'm not trying to dissuade you, btw - just making you aware of potential issues.
If you decide to let her continue incubating, you'll want to create a micro-environment for BB and eggs. As was mentioned, maintaining acceptable humidity levels in a tank can be problematic in general...but it's a must with eggs. If they get too dry, the babies could die early or simply fail to hatch.