Personally id do a soil & play sand mix in a larger container its recommended depth is 12inches, remember to keep it moist it needs to hold the hole without collapsing, though some girls are really fussy compared to others, so the plant option in there could be used by her also in soil so keep moist but not soaking wet, they do require alot of privacy at this stage, but remember to keep a sly eye on her but without disturbing her as can put her off. Also remember some females love to do test holes 1st which they will dig cover up & deposit nothing. Laying eggs doesn't come easily to some females so is a nerve-wracking time especially your 1st experience & the females 1st combined. Your start to notice when she ready, she show receptive colours 1st, she will pass around more & can usually notice increased weight gain.. hope that helps