Jan, thank you for your question. There is an important distinction to be made between "plus or minus" and "plus a negative number," for example. Yes, a multipurpose indicator (dot 5) must come between the two operation signs when they are printed side-by-side. All of the examples you write about must have a dot 5 between the two signs, otherwise they will be read vertically. See Nemeth Code Section 134 on page 132 to read the rule and see four examples.
Note that sometimes the print copy will show the second sign slightly raised. If this is what your worksheet shows, you should braille each raised symbol as a left superscript. If your student is not used to seeing this arrangement, encourage the vision teacher to teach it because this is how it is (correctly) brailled on standardized tests. It would do the student a disfavor to have her see it for the first time in a testing situation.