@slyytherinn I'm not sure which NRaas mod(s) you're using, so I'll describe how to try to fix the issue without mods. If the interventions don't help, we can talk about mod-related solutions.
Start by deleting the five cache files in your game folder in Documents. They should be deleted on a regular basis anyway, and especially now that you're having issues. While troubleshooting, be sure to delete them every time you quit the game, whether a workaround helped or not. For reference, those files are:
- CASPartCache.package
- compositorCache.package
- scriptCache.package
- simCompositorCache.package
- socialCache.package
First, load your game and change the toddler age slider so that the kid has a couple of days left before her birthday, then use "save as" to rename the save, quit, delete your caches, and reload. Instead of blowing out the candles, you can try using a cheat to force the toddler to age up. This can be done with NRaas MasterController; the non-mod way is to bring up the cheats console (crtl-shift-c) and enter "testingcheatsenabled true" without quotes, then shift-click on the sim and select "trigger age transition." This sometimes works when the birthday cake doesn't. Try waiting a day as well.
If this doesn't help, you can quit without saving. After you reload, take the toddler into CAS, either by using NRaas MasterController or testingcheats—a shift-click on the sim will show the option to "Edit in Create a Sim." Pick entirely new outfits and hairstyle(s); be sure to use only base game items. Even if you don't have any custom content, her outfit assignments could be broken. Once you're done, "save as," quit the game, delete your cache files, reload, and see if you can age her up.
If this doesn't work, try evicting and replacing the sim household, this time after you've changed the toddler's outfits. The more thorough way to do this is to evict the sims, save their house to the bin, bulldoze the lot, replace it with its bin copy, and move the family back in. Then "save as," quit, clear your cache files, and reload.
If this doesn't help either, try temporarily moving out the toddler with an adult. You only have to leave them in a different house for a sim-day or so, but be sure to quit and clear the cache files before bringing them back. You could also try to trigger an age transition on the toddler while she's living elsewhere, although you'll have to stop "watching" her, i.e. move the camera away from her, and wait until the next morning to find out whether it worked.