You have my sympathy, those tantrums are terrible. It is scary because you can be aware you may hurt them in the way they can thrash about etc.
Can I really recommend a book called The Parenting Puzzle. I hate reading and am dyslexic but this is a dip into and out of book and a huge help.
www.familylinks.org.uk/shop/schools-shop/the-parenting-puzzle
She may well grow out of this and if she does not you will need to explore more what drives the tantrums. I am sure most kids do grow out of them.
My dd was/is similar in that bribery does not work. I am now grateful for this, it means in later life people will not be able to buy her off (I hope). My dd also knows her own mind and her difficult phase was age 5-7. But I saw occasional tantrums well before that.
Try and anticipate the tantrums and minimise the impact by making sure you are in as safe a place as possible when they happen. Sometimes we do know what will set our kids off and I have sometimes moved delicate or special items (not that we have many!) in readiness for an argument!
You are not being unreasonable at all. Kids can be hard work and can scare us, not always that we think they will hurt us (although they can, my dd has nearly headbutted me in the face by accident!) but more because we can (in trying to restrain them) hurt them. In the clamer moments can you talk about the good behaviour, emphasise the good and head tantrums off at the pass when you can. It is not 'giving in' or not being tough enough it is helping children to deal with their very real feelings.
If this rage continues I would speak to the health visitor, explore if any food are making it worse (e.g. keep a food and behaviour diary to see if this impacts it - e.g. sweets or whatever making it worse) and I would also look out for books like
What to do when your temper flares
But that really is for the future and it may all change by then. I do think keeping a record of 'incidents' helps if you can as some things may be making it worse. My ds (4) is worse when he has too much TV and my dd (now 10) is worse if we go out too much!