Suck on her own nipples
Suck on her own nipples is a tit-oriented stimulation, a more extreme type of self nipple stimulation than selflicking. The effect of applying a vacuum on the nipples rather than simply licking the nipples, seems to produce more enjoyment. However to suck on her own nipples, a huge breast size is required: The minimum requirement are medium tits, however big tits and very big tits make things even easier and require less bending of her neck.
This is how sucking on her own nipples is done: While continuing to breath through her nose, she encloses one of her nipples with her lips and then produces low pressure in her mouth. The low pressure will automatically pull the nipple into her mouth, while at the same time erecting her nipple. Depending on the degree of her experience on selfsucking her nipples, she might give her nipple additional stimulation by touching her nipple with her tongue. Sucking on her own nipples is often performed during nipple masturbation.
Photos of Girls sucking their own Nipple
Further reading: Girl sucking nipples