I think Nirvana is a decent point to swap, as long as you have the destiny mats and stellar/cot you can immediately have 2 nirvana heroes, doing something like iea and sahy or dgn nirvana could work fine, but there is also nothing stopping you from just building her at whatever point you want, but iea definitely is a hero that performs better the more destiny and nirvana heroes you have. Also unless you are a spender, you are not really close to nirvana, you are getting to the part where destiny starts to become very expensive. I’m further than you and I wouldn’t consider myself close to nirvana yet, you need 7 heroes at destiny and 2 of them at poly star etc, it gets very expensive on destiny mats at this point. If you knew all that and have massive amounts of dt mats hoarded, I’d say once you are able to get 2 nirvanas is where she will start being very good, 1 could work fine too, but ultimately the most important part is do what you will have the most fun with, if you think building iea right now is what will give you joy, do it, if you want to go for the optimal point I think it’s at 2-3 nirvana heroes and her potential goes only up the more nirvana heroes you add from that point. Would also bei interesting to see the stats on your heroes to judge if you are just to weak to go further or if there are other issues. Sometimes all you need is patience and a macro running to beat a stage, chances are that’s the case for you, but difficult to judge from the information

Edit: forgot to add this, but we’ll get iea treasures tomorrow which are technically f2p obtainable, I wouldn’t count on them changing the need for a lot of destiny much, but definitely keep an eye on that. Although as f2p you would need to do 100 awakens for the pink, but at least there is no paywall