Honestly, I would just ILL. If that is the only ride you do an ILL, maybe it is not too cost prohibitive? Any other option is going to require waiting in a long line, going SR, or getting a
DAS. RD is not a great option, unless you have hotel guest EE and use that time just to stand in line until RSR opens at regular park opening time (IF it opens at park opening), as OP said. Maybe you can ILL this ride and save money elsewhere in the trip if this is the priority for your Mom.