Hiya,
Mate the things are different in different EU country. Mine was Hungary and they have a special immigration office which attested the invitation letter and sent it to me and then I sent it to embassy. It took 3 weeks to get the visa including the invitation letter.
I have checked this on austrian embassy
http://www.bmeia.gv.at/en/embassy/londo ... ermit.html
II) Niederlassungsbewilligung (for foreigners who plan to live in Austria for a longer time period = Permanent Residence Permit), i.a.
• any purpose, private reasons (e.g. move to Austria in retirement)
• employment or self-employment under certain circumstances
• family members of aliens living in Austria, family re-unification
I know she is not your family memebr but might be being your girlfriend will do the work.
Or
V) Family members / Dependants
1) Which residence permit can be obtained by family members / dependants of Austrian, Swiss and EEA citizens not entitled to the right of unrestricted mobility?
(q.v. 7))
Family members (spouses und unmarried minors children, including stepchildren and adopted children) of Austrian, Swiss and EEA citizens not entitled to the right of unrestricted mobility (and not EEA or Swiss citizens themselves) can obtain “Niederlassungsbewilligung- Familienangehöriger” (settlement permit – family member), exempt from the general immigration quota. This settlement permit allows a third country nation unrestricted access (-> § 1 Paragraph 2 lit. I AuslBG) to the labour market in Austria. -> § 47 Paragraph 2 NAG
Following other relatives of Austrian, Swiss and EEA citizens not entitled to the right of unrestricted mobility (and not EEA or Swiss citizens themselves) can obtain a “Niederlassungsbewilligung - Angehöriger” (settlement permit – dependant), exempt from the general immigration quota (-> § 47 Paragraph 3 NAG):
- Next of kin of Austrian, EEA or Swiss citizens or spouse in direct ascending line (parents and parents-in-law)
- Partner of an EEA citizen, whereupon the existence of a long-time relationship in the country of origin has to be proven and alimony is actually granted
- Other relatives, who have already lived in a common household with an Austrian, EEA or Swiss citizen in the country of origin and have already received alimony
- Other relatives of an EEA citizen, who are in urgent need of personal care due to severe causes
Please note: A “Niederlassungsbewilligung – Angehöriger” (settlement permit – dependant) does not authorise the acceptance of employment. Furthermore, to obtain this type of residence permit the Austrian, EEA or Swiss citizen has to submit a statement of financial liability.
2) Are family members / dependants of Austrian, Swiss and EEA citizens not entitled to the right of unrestricted mobility allowed to submit their application for an “Erstniederlassungsbewilligung” (first-time settlement permit) in Austria?
Family members (nuclear family) are allowed to apply in Austria if they entered Austria legally and are legally allowed to stay on Austrian federal territory (i.e. the allowed period of stay without visa or the validity of the visa has not yet expired). -> § 21 Paragraph 2 Z 1 NAG
Other dependants (as all other applicants) are only allowed to file their application in Austria if they are allowed to enter Austria without a visa. -> § 21 Paragraph 2 Z 5
How do I assure them of that apart from a letter from my employer mentioning that I am on holidays and am expected to return to work on the mentioned date? 
For my next application I am planning to give them either a full itinerary of my travel in coming months (they only ask for flight bookings and not actually tickets -which again puzzles me as to what exactly they mean by bookings not tickets ? For accommodation, I'd be staying with my girl friend anyway apart from one instance where we are travelling outside Vienna.
I risk this whole headache annoying my girl friend more than the Austrian Embassy and we may have to decide to break up 