Perhaps you could get her singing! Just very simple songs to begin with (2/3 pitches and simple rhythms). This will provide her with some musical material with which you could work later - playing the tunes in different keys on the piano, learning the rhythm names for the song. If possible the songs should have movements so that she can experience the pulse with as many different movements as possible. Get her to find her heartbeat and show the speed by opening and closing her hand and saying, 'bmm, bmm' in time with it. Ask her to show a faster or a slower heartbeat. Ask her if she has a heartbeat then if she thinks a song has a heartbeat - demonstrate to her that music has a heartbeat too and that a song comes alive in this way when you sing it and move to it.
Lucinda Geoghegan's 'Singing Games and Rhymes for the Early Years' (published by the National Youth Choir of Scotland) has a lot of excellent repertoire. The book also makes clear what concepts and skills are being developed by each song or rhyme. Most importantly you need to develop her feeling for pulse, an understanding of the difference between pulse and rhythm and the ability to differentiate between pitches. These skills will prove invaluable for when she starts learning the piano.
You could tell her a story which you 'illustrate' with improvisations on the piano - a Dalcroze colleague of mine used to tell one about being in your bedroom late at night and not being able to sleep. So you got up and opened the curtains and looked out into the moonlit garden. You crept downstairs and out in the garden where you skipped and played with various animals - then retraced your steps back to bed. Everything had its own piano 'signal' - ie a sound for opening the curtains, another for the moonlit garden, another for creeping down the stairs, various ones for the different animals etc. and the child 'acts out' the story to the musical signals. This story is particularly good as it then works in reverse and you eventually don't have to tell the child that this is the creeping back upstairs part as they will just recognise the music and act accordingly. Brilliant for developing musical memory, differentiation of various types of music and responding with movement to the sound heard.
You could improvise a melody of just crotchets for her to walk in time with - quavers indicate jogging, dotted quaver/semiquavers indicate skipping and minims are striding/slow walking. You could incorporate this rhythm identification and movement into the above story (or your own/her own stories).
Those are just a few Kodály/Dalcroze suggestions - hope this is helpful.