ANSWER - While not every witch can trace her lineage back to another witch it is generally acknowledged that an aptitude for witchcraft can be passed down a bloodline. It is important to make the distinction between being "born" a witch and being born with a natural disposition toward using the gifts associated with witchcraft. Simply put - you are not a witch until you practise witchcraft.
It is certainly possible that if your mother is a practising witch you may have inherited some degree of ability from her. However these gifts will not develop unless you actively seek to practise and work with them. You say that you fear this woman so with this in mind it may well be a good idea to start working some basic spells and protective magics as it may have the dual benefit of reducing your fear and also getting some tangible defence between your mother and yourself.
It is hard to pin down what type of witch your mother is with the information you've provided. I'm assuming you want to know if she is likely to practise the kind of aggressive magic that may cause harm to others. Unfortunately the fact that she practises magic in her own self interests isn't proof that she would choose to take this further to the extent of targeting others with her magic. Most witches - even the whitest of Wiccans will use magic to some degree for personal gain. But - try to think about what kind of personal gain your mother uses magic for. A witch who casts to maximise her own luck, ability and circumstances may have a very different moral outlook to a witch who casts to reduce those of another. Take as an example the magic used in getting a job. One witch may employ magic to prove her own chances of success, another might take the opportunity to make all the other candidates appear less attractive. Both spells could be classed as personal gain but there is a clear difference in the morality of the casters.
As with most spells the proof of the pudding is in the eating and by this I mean the best way to determine if you have been cursed is to assess any evidence that may support a cursing, A serious curse may have implications in every area of your life. If your love life, your health and your job have all taken a serious turn for the worse then it is possible that she has placed a curse on you. If however you have noted no noticeable change in any of the areas in your life then either she has not cursed you or she's not very good at cursing.
I do think it is important to distinguish between a run of bad luck and the natural peaks and troughs that all of us go through in our lives. Think rationally - is your life falling to pieces with no obvious cause? Try not to attribute natural lifecycles to magic. Only if everything is inexplicably and significantly wrong would I advise seriously considering the fact that you have been cursed.
Could you not try and have a conversation about this with your mother? I appreciate that given the nature of your question the relationship between the two of you probably isn't great but she might respond to your interest in witchcraft - especially if you are feeling called to a similar path yourself - I wonder if this might
be a way of getting to know her on a deeper level and one which may help to put some of your fears to bay? I don't think I or anyone else can presume to advise you on this without being party to a lot more information about the history of the relationship between you and your mother but I would suggest you give some consideration to having an open conversation with her about what she does and the gifts you may have inherited from her.
(If after thinking this all through you do genuinely feel you may have had a curse placed on you - send me another question and we will address how to best tackle the problem).