Hi.
Thanks for your query.
This looks to be post-traumatic, meaning after a trauma.
Dark purple
bruise with a lump is suggestive of a
hematoma.
It is possible that she does no remember how it occirred as it would have bben mild
Because of the typical fat distribution in this area, it was not noticed easily.
If this is bruise , the treatment is conservative.
Anti-inflammatory medicines would help if given in a proper dosages.
IF it is not painful, if the local temperature is not raised you can have have '' a wait and watch '' policy.
Keep it under observation and will settle in one to 3 seeks time.
If you are suspicious of an infection , you have to start her on an antibiotic and anti-inflammatory medicines.
yes, you should be concerned about this.