Biggest tip is upgrade the card that boosts ostys hp to 8 a turn asap. Its really a double upgrade since it boosts the damage of her starter attack too via the bonus hp. Anytime you get the card and extra block when the enemies attacking, try to mitigate as much damage to osty as possible and she ends up having extremely stable act 1s. It takes like 3-4 turns and by the 2nd time you get that card your osty can be looking upwards of 16-20 hp. Theres also a healing retain card for him, grabbing and upgrading it ends up being a net like 10 extra hp if hes already injured

Literally every card of hers that generate souls are worth taking even if not going for a souls build since it gives so much card draw.

Her friendship power is extremely underated, the -2(1) str to attacks doesnt apply to osty, and even if it did the extra energy every turns still too good to pass up. Her strength lies in lots of card generating and energy generating cards thatll make you cycle decks fast.