sed add space X times

Pattern:
Mary walks at the park every day with her children


will make it add 1 space at the end (trailing)

I want to add X ($VARIABLE) number of spaces (which comes from RANDOM)

i.e.
VARIABLE='14'
then it will do:
= 14 spaces added at the end.....

Some suggestions how to do that?

I tried to do it adding unicode xA0 but it didn't work

Thanks!