in answer to your question,
ringnecks are very territorial birds and very against other species, it isnt advisable to ever house them with anything but ringneck parakeets...
i have to ask how you know the male is infact a male ? have you had him dna sexed? the reason i ask this is that ringnecks can not be sexed visually until they are 3 years old, the females can be sexed sooner but males as a rule do not show their rings until they are sexually mature at 3 years old,
females can be mature fully at around 18 month to 2 years old,
if she was an aviary bird before you had her even as a chick they can be very agressive, if she was hand reared and was aggressive when you had her from a chick the chances are whoever hand reared her didnt do a very good job,
if you are planning to breed from her you need a male that is 3 years or over , they must be introduced togather before adding them into the same cage and preferably the cage should be unfamiliar grounds, the female will be very territorial of where she is now,
you will first need to get them aquaionted by putting the cages next to each other for a few weeks or so , then once they interact with each other , and make the general noises without trying to gouge each others eyeballs out through the bars , then you can try them in the same cage, preferable to add them to a new cage as said before becase of territory issues, add them in the morning when they have time to get used to each other and establish dominance between them (yes they may have a peck at each other and some cases draw a slight bit of blood but anything bad (a watchful eye on them is needed!!!! ) and the bird will need to be removed, they will need a short fight to establish dominance but when they do it it shouldnt last long, otherwise they may just get on like a house on fire and start preening and feeding straight away, each bird is different ...
i would suggest however not to keep her or him for that matter in with any cockatiels, you may find she settles down a lot away from them, and if planning on breeding then yo definitely must keep all other birds apart from 1 male ringneck, seperate!!!! otherwise any other bird in the cage with them will end up well their will be a severe bloodbath , and almost certainly a fatality, !!
cockatiels are very gentle birds and will get on with a lot, however budgies are very nippy spiteful birds and hold their ground, and budgies almost certainly have caused an awful lot of fatalitys when mixed in with other species of birds... ringnecks are likewise the same ,
all to be kept species only, yo do get the odd exeption but trust me the odds are really not worth the risk..
good luck with your birds, you have a long way off before you can breed from them and so a lot of time to prepare ....if you need any info just ask, their is a thread on here to which i replied with some info about ringnecks and breeding if you have a search through other pets and animals you will find it, good luck and if you have any more questions please ask
katie