Possible for db to solo pb?

No cigar.
Assuming 60-40 ratio in a party of 6 without HS: (20% + 80%*200/1200) * 62,900,000 = 20,966,666.7
Dunno where she got 21,399,998 from. Maybe the new formula isn't exactly what we used to have? Otherwise, the party must have had a lvl 141ish instead of all 200s. But even then, the numbers don't quite match up.

The party bonus (6419700) is about 30% of her white exp. Assuming a party of 6, the bonus should be 77.15% if I'm not mistaken?

you cant assume its a party of all 200s
Maybe she has sign up mules inside that arent 200
this might explain the exp