First of all, if you allow the hitting to 'work' i.e. by letting the person or object get away from your daughter when she hits, this is rewarding the behaviour. Hitting people or pushing them is normally quite successful in removing them. She's using hitting as an escape behaviour. As much as you can, just block the hitting and keep the object or person close by so that the hitting will not be a successful strategy for her.
If she cannot talk at all, you can teach a more appropriate request for things to finish or go away, for example shaking her head, or making a 'no' hand gesture (e.g just showing you the palm of her hand). You can teach this by presenting her with something you know she won't like and would normally make her hig(for example, yucky food) and IMMEDIATELY (i.e. BEFORE she hits) physically prompt her to make a gesture that means 'no.' Pair this with language i.e. you say 'no thanks mummy' as she makes the gesuture then immediately take it away. Keep practising this and praising her for telling you nicely. While she is learning, always honour her request if she asks appropriately. While you'll need to hold her hand at first, you can gradually fade this back, e.g. by holding her wrist, then her elbow etc. As you are holding her hand, she should not be able to hit at the same time, but if she does hit then do not remove the object. She will soon learn that hitting doesn't work and appropriate communication (signing) does. Basically, never allow her to get what she wants by hitting.
If she cannot talk at all, it may be worth teaching her some more signs to ask for things she wants (look up baby signing on youtube). If you'd like some advice on how to teach signs to babies, or with any other behaviour issues please contact me - I am an experienced applied behaviour analyst.