Would someone knowledgeble please answer me? I need to know before I do this!
Thank you in advance for your help!

They separate very well if the parent is big enough. The key is to try to get the division proportional, as long as you balance out the amount of roots with the size of the top plant at least somewhat you'll be OK...depending on how its growing your hibiscus is probably going to have some taproots, but I would only really concern myself with digging up a sane amount of those. The roots are really muscalagious (feel slimey) amd can hold a lot of water and nutrients, so division really doesn't harm them.
Hope that helps.
Peace

Thank you so much! I'm reassured that if I'm careful I won't kill her part or mine, which would be a shame because it's so beautiful all summer into fall. Its still blooming even now! Thanks again. I appreciate your time and knowledge.

No problem, also, until it gets too cold for water try to keep the root systems on the new plants pretty moist...these plants are part-time marsh dwellers and the do much better if they're roots can get well established before freezing. (They do however handle even the worse saturated frozen ground; one of the biggest naturalized stands around my area is in a drainage ditch which is submerged and has road salt and car exhaust beating it and every summer the patch just gets bigger)