I'm enemies with Mr. House since I went to the Legion camp and blew up the underground reactor, I needed to take Cass with me to do one of the quests for the Van Graffs, so I sent Veronica back to the Lucky 38. After finishing the quest with the Van Graffs and heading to the 38, the securitrons shoot me on site and when I go up to the presidential suite, Veronica isn't there, even if I sleep for a couple of days. Will she come here once I clear out the place of securitrons or kill Mr. House?

If your playing on hardcoe, then there is a good chance she was killed upon entering the Lucky 38. You may want to look for her body. Otherwise:

Thats a good idea, if it doesnt work you can try killing Mr. House. Companions take their sweet time getting back to the Lucky 38, they seem to walk instead of run. I am not sure what happens if you send a compaion home from across the river. They may not be able to get back to the Strip. You may want to check the exit area of the Legion camp if you released her over there. It took ED-E an entire day to get to the Strip from Primm in my game. I suggest never sending the compaions back to Luck 38, but instead to their homes. You can just Fast Travel to pick them up.