A few concepts that aren’t completely ready to go but I’m thinking of messing with.
Apollo’s noble phantasm
Since Olga’s the one in control as a Psuedo servant her Noble Phantasm are based off of the grandor she often used.
The attack itself is a suicide attack type that itself is a reflection of Olga’s infinite death loop. It’s one that will result will wake Olga from her ‘dream’ and return her to her death loop. It’s capable of trapping the target in that very same death loop as well. (?)
Apollo being a dream
Olga as a psuedo servant is driven by the dream of achieving the recognition she believes she deserves for her accomplishments. However, over the course of her death loops shifted from that to getting revenge against Levi and enacting it by making him suffer the very same fate as her own.
As for her awareness as a dream, it is something that Olga is aware of. She knows that she isn’t actually really here because the grail or the god apollo felt pity on her and that she is in fact still experiencing her death loop. It’s information she doesn’t exactly take to well at first but is something she comes to accepting so long as she can drag Levi into the personal hell he trapped her in. It’s not exactly information she’s likely to share with anyone until she’s accomplished her revenge.
If she comes up with another dream for herself it’s possible for Olga to be re-summoned after using her noble phantasm. (?)