Hello,
I'm a KS1 teacher. One important piece of advice I give to all parents who are concerned about how their children are progressing is to remember that all children progress at different rates and the children who have seemingly progressed ahead of her may plateau while your DD speeds ahead of them later in the year.
It can also be helpful to take a more relaxed approach to helping with your DD's maths learning outside if school. If children are struggling and, as you mentioned your DD is feeling, demoralised they can feel pressurised by more work at home leading to further loss of confidence and their interest for the subject will decline. Try to sneak maths into your daily routine: counting pegs when doing the washing, adding food items at dinner time, finding coins when buying sweets etc. This way your DD will be doing lots if adding without feeling like she is doing more work ( work she doesn't feel she can do).
Your child's teacher has said your DD should be using other methods and this is fine but ultimately your DD. Should be using methods she feels comfortable with. If she has to struggle with using an unfamiliar method to help her solve sums she is dealing with two problems- the sum and the method. New methods can be introduced and reintroduced occasionally as choices your DD can make to help her solve addition problems and, if fine on her terms, het confidence in using them will grow as will her ability to solve sums.
Other methods to try are: practical methods (eg. buttons, Unifix cubes, Lego etc), numberlines, hundred squares, pictures ( draw 5 sweets in one jar, 2 in another and count them).
Knowing number bonds obviously will help but your DD needs to know what they mean. Making bonds with practical equipment can help eg. Hiw many ways can we make 10 with these buttons?
Make maths a game rather than work. Building your DD's confidence us your first aim, enjoyment and attainment should then follow.
Ask to speak to the class teacher to find out what maths they are working on each week and what methods they ate using in class.
I hope some of that helps.