Arena tour session prep for for super-quiet singer

Hi all. Need to prep a bunch of vocal mixes for a live tour. The shows are 6,000 - 10,000 indoor arena size and are with a singer who is an amazing studio vocalist, but is super quiet live.

FOH engineers always have quite a hard time getting her loud enough without feedback - even with carefully chosen mics, stage positions, IEMs - all the tricks. There is no live band on stage, just electronic instruments. On the last tour, the FOH engineer had some success bringing everything else down but could be something of a vibe killer.

So for this next tour, everyone is resigned to relaying on track a bit more heavily.

Are there any particular methods to prepping a tracked 'lead' vocal that can be blended with the real lead vocal to taste, without getting a load of aliasing / obvious doubling? Or, is it a case of using 100% track vocal, or 100% live, but avoiding a mix of the two? Obviously BVs, doubles etc will run on track, I'm talking about the lead vocal though.

Thanks for any advice!

PS: If there exist any good tutorials out there, please just point them my way - more than happy to do my own research rather than counting on y'all, but I've found it incredibly difficult to find anything on this topic from anyone half legit. Assume this is because most producers can't really throw artists under the bus by showing how much track vocal they have in their live mixes... but anyway, if there is an SOS article or similar I have missed, please point it my way.